fix: encode forkid entry in struct, accept trailing fields (#3193)

crates/net/discv4/src/lib.rs

@@ -35,6 +35,7 @@ use reth_primitives::{
     bytes::{Bytes, BytesMut},
     ForkId, PeerId, H256,
 };
+use reth_rlp::{RlpDecodable, RlpEncodable};
 use secp256k1::SecretKey;
 use std::{
     cell::RefCell,
@@ -1967,14 +1968,56 @@ pub enum DiscoveryUpdate {
     Batch(Vec<DiscoveryUpdate>),
 }
 
+/// Represents a forward-compatible ENR entry for including the forkid in a node record via
+/// EIP-868. Forward compatibility is achieved by allowing trailing fields.
+///
+/// See:
+/// <https://github.com/ethereum/go-ethereum/blob/9244d5cd61f3ea5a7645fdf2a1a96d53421e412f/eth/protocols/eth/discovery.go#L27-L38>
+///
+/// for how geth implements ForkId values and forward compatibility.
+#[derive(Debug, Clone, PartialEq, Eq, RlpEncodable, RlpDecodable)]
+#[rlp(trailing)]
+pub struct EnrForkIdEntry {
+    /// The inner forkid
+    pub fork_id: ForkId,
+}
+
+impl From<ForkId> for EnrForkIdEntry {
+    fn from(fork_id: ForkId) -> Self {
+        Self { fork_id }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
     use crate::test_utils::{create_discv4, create_discv4_with_config, rng_endpoint, rng_record};
     use rand::{thread_rng, Rng};
     use reth_primitives::{hex_literal::hex, mainnet_nodes, ForkHash};
+    use reth_rlp::{Decodable, Encodable};
     use std::{future::poll_fn, net::Ipv4Addr};
 
+    #[test]
+    fn test_enr_forkid_entry_decode() {
+        let raw: [u8; 8] = [0xc7, 0xc6, 0x84, 0xdc, 0xe9, 0x6c, 0x2d, 0x80];
+        let decoded = EnrForkIdEntry::decode(&mut &raw[..]).unwrap();
+        let expected = EnrForkIdEntry {
+            fork_id: ForkId { hash: ForkHash([0xdc, 0xe9, 0x6c, 0x2d]), next: 0 },
+        };
+        assert_eq!(expected, decoded);
+    }
+
+    #[test]
+    fn test_enr_forkid_entry_encode() {
+        let original = EnrForkIdEntry {
+            fork_id: ForkId { hash: ForkHash([0xdc, 0xe9, 0x6c, 0x2d]), next: 0 },
+        };
+        let mut encoded = Vec::new();
+        original.encode(&mut encoded);
+        let expected: [u8; 8] = [0xc7, 0xc6, 0x84, 0xdc, 0xe9, 0x6c, 0x2d, 0x80];
+        assert_eq!(&expected[..], encoded.as_slice());
+    }
+
     #[test]
     fn test_local_rotator() {
         let id = PeerId::random();

crates/net/discv4/src/proto.rs

@@ -1,6 +1,6 @@
 #![allow(missing_docs)]
 
-use crate::{error::DecodePacketError, PeerId, MAX_PACKET_SIZE, MIN_PACKET_SIZE};
+use crate::{error::DecodePacketError, EnrForkIdEntry, PeerId, MAX_PACKET_SIZE, MIN_PACKET_SIZE};
 use enr::{Enr, EnrKey};
 use reth_primitives::{
     bytes::{Buf, BufMut, Bytes, BytesMut},
@@ -306,7 +306,7 @@ impl EnrResponse {
     /// See also <https://github.com/ethereum/go-ethereum/blob/9244d5cd61f3ea5a7645fdf2a1a96d53421e412f/eth/protocols/eth/discovery.go#L36>
     pub fn eth_fork_id(&self) -> Option<ForkId> {
         let mut maybe_fork_id = self.enr.0.get(b"eth")?;
-        ForkId::decode(&mut maybe_fork_id).ok()
+        EnrForkIdEntry::decode(&mut maybe_fork_id).ok().map(|entry| entry.fork_id)
     }
 }
 

crates/net/network/src/discovery.rs

@@ -2,7 +2,7 @@
 
 use crate::error::{NetworkError, ServiceKind};
 use futures::StreamExt;
-use reth_discv4::{DiscoveryUpdate, Discv4, Discv4Config};
+use reth_discv4::{DiscoveryUpdate, Discv4, Discv4Config, EnrForkIdEntry};
 use reth_dns_discovery::{
     DnsDiscoveryConfig, DnsDiscoveryHandle, DnsDiscoveryService, DnsNodeRecordUpdate, DnsResolver,
 };
@@ -100,7 +100,8 @@ impl Discovery {
     #[allow(unused)]
     pub(crate) fn update_fork_id(&self, fork_id: ForkId) {
         if let Some(discv4) = &self.discv4 {
-            discv4.set_eip868_rlp("eth".as_bytes().to_vec(), fork_id)
+            // use forward-compatible forkid entry
+            discv4.set_eip868_rlp("eth".as_bytes().to_vec(), EnrForkIdEntry::from(fork_id))
         }
     }